If you have granite countertops in your home, you might consider testing them for the amounts of radon gas they give off, experts say, due to the potential that those amounts are above levels considered safe.

But marble manufacturers say flat-out that, "Radiation in granite is not dangerous."

Radon is "a cancer-causing natural radioactive gas that you can’t see, smell or taste," the Environmental Protection Agency explains on its Web site. "Its presence in your home can pose a danger to your family's health. Radon is the leading cause of lung cancer among non-smokers. Radon is the second-leading cause of lung cancer in America, and claims about 20,000 lives annually." The popularity and demand for granite countertops has grown in the last decade, as have the types of granite available.

The amount of radon in the air is measured in "picoCuries per liter of air," or "pCi/L," and the EPA says 4 pCi/L is the level of radon exposure that requires someone to take action. The agency also says levels lower than that "still pose a risk" and "in many cases, may be reduced."According to The New York Times, 4 picocuries is "about the same risk for cancer as smoking a half a pack of cigarettes per day."

The newspaper also reports that, "Allegations that granite countertops may emit dangerous levels of radon and radiation have been raised periodically over the past decade, mostly by makers and distributors of competing countertop materials. The Marble Institute of America has said such claims are "ludicrous" because although granite is known to contain uranium and other radioactive materials like thorium and potassium, the amounts in countertops are not enough to pose a health threat.

Indeed, health physicists and radiation experts agree that most granite countertops emit radiation and radon at extremely low levels. They say these emissions are insignificant compared with so-called background radiation that is constantly raining down from outer space or seeping up from the earth's crust, not to mention emanating from manmade sources like X-rays, luminous watches and smoke detectors.But with increasing regularity in recent months, the Environmental Protection Agency has been receiving calls from radon inspectors as well as from concerned homeowners about granite countertops with radiation measurements several times above background levels."

On The Early Show Friday, Stanley Liebert, quality assurance director at CMT Laboratories in Clifton Park, N.Y. showed co-anchor Harry Smith a chunk of granite countertop emitting 4.4 pCi/L and said, "The probability is we're looking at a problem here, and the granite would actually be removed.

"In the lower levels," Liebert said, "we can usually improve (radon levels) by exchanging air" with systems that "bring fresh air in and exchange it with the air in the kitchen."He says some granite countertop colors are more potentially troublesome than others: "We're seeing higher results in reds, pinks, purples. However, you've got to test them all.

"The only way to know about radon levels from your granite countertops, and in your home in general, is to test for them, and the EPA says, "There are many kinds of low-cost "do-it-yourself" radon test kits you can get through the mail and in hardware stores and other retail outlets. If you prefer, or if you are buying or selling a home, you can hire a qualified tester to do the testing for you. You should first contact your state radon office about obtaining a list of qualified testers. You can also contact a private radon proficiency program for lists of privately certified radon professionals serving your area."